1. Field of the Invention
The present invention generally relates to a thin battery. More specifically, the present invention relates to a thin secondary battery having an electricity-generating element housed inside a battery outer casing and having foil-like electrode terminals.
2. Background Information
A battery is a device that produces electricity from a chemical reaction. A battery can be either a single cell or can include several cells connected together in series or parallel. A battery cell typically has one or more positive electrode, one or more negative electrode plates, one or more separators, and an electrolyte contained within a battery outer casing, and a positive electrode terminal and a negative electrode terminal protruding from the battery outer casing. The electrolyte may be aqueous (composed of water) or nonaqueous (not composed of water). When an external load is connected to the battery cell, the negative electrode supplies a current of electrons that flow through the load and are accepted by the positive electrode. This reaction continues until the external load is removed.
A secondary battery is commonly known as a rechargeable battery. In a secondary battery, a non-aqueous electrolyte is typically used, which is composed of organic liquids and salts of lithium to provide ionic conductivity. Thus, a secondary battery using a non-aqueous electrolyte has a much higher cell voltage than a battery using an aqueous electrolyte.
Recently, batteries have become thinner, smaller, and lightweight. Since thin batteries are small and lightweight, a plurality of thin batteries can be connected together and combined into a battery pack that provides high voltage and high capacity (e.g., Japanese Laid-Open Patent Publication No. 9-259859).
The positive and negative electrode terminals of the thin battery disclosed in Japanese Laid-Open Patent Publication No. 9-259859 are foil-like terminals made of such materials as aluminum foil and copper foil. Consequently, when the terminals are connected together to make a battery pack, the stress generated in each terminal concentrates along the line where the terminal connects to the battery outer casing, causing the terminal to be easily broken.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved thin battery. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.